When learning computer networking it is essential to have a general idea of the different computer networking reference models and the reasoning behind the layered approach. Both the TCP/IP network model and the OSI Model create a reference model for computer networking. The OSI model is widely used to teach students as was created in the mindset of a reference book. The TCP/IP standards were created to provide guidance to people actually implementing a networking technology and was created in the mindset of a service manual. Much like the answer to the question of why was the internet created, the answer to why do we need the OSI model depends on who you ask. Here at ComputerGuru.net try to explain the basics of the OSI model as it relates to understanding basic computer networking.
The Internet and the TCP/IP family of protocols evolved separately from the OSI model. Often you find teachers, and websites, making direct comparison of the different models. Don't get too hung up on drawing direct comparisons between the two models. Our discussion here on the two networking reference models is address some commonly asked questions, and give some historical perspective as to how the models have evolved.
The Open Systems Interconnection Reference Model (OSI Reference Model or OSI Model) was originally created as the basis for designing a universal set of protocols called the OSI Protocol Suite. This suite never achieved widespread success, but the model became a very useful tool for both education and development. The model defines a set of layers and a number of concepts for their use that make understanding networks easier. The theoretical OSI Reference Model is the creation of the European based International Organization for Standardization (ISO), an independent, non-governmental membership organization that creates standards in numerous areas of technology and industry. The OSI model was first published in 1984 as ISO 7498: Information processing systems -- Open Systems Interconnection -- Basic Reference Model.
The Internet model is often compared to the OSI model. This internet model has many names such as the DOD reference model or the ARPANET reference model, because like the internet itself the TCP/IP protocol suite has evolved over the years. The ARPANET was the original name of the network we now call the internet. ARPA, currently known as DARPA, the Defense Advanced Research Projects Agency, is funded by the DoD (Department of Defense).
Unlike the International Standards Organization (ISO) where there is one main library of information that maintains specific standards, the internet is an ever evolving network with many entities working together to maintain standards. There is a collection of documents known as Request for Comments (RFC) maintained by the Internet Engineering Task Force (IETF) that describes various technology specifications.
Simple talk and some needed geek speak
Since TCP/IP is the primary networking language of the internet, everyone who works in the field of technology needs to have at least a simple understanding of how it works and its role in the big picture of the internet. In the spirit of the Guru 42 family of websites, we attempt to tackle the basic understanding using as simple terms as possible.
To understand the role of TCP/IP in the big picture of the internet, we need to delve just a bit into the geek speak of the internet. If you want to learn more, and really delve into how the internet works and the interesting history of the internet, an understanding of IETF and RFC's.
What is an RFC?
The concept of Request for Comments (RFC) documents was started by Steve Crocker in 1969 to help record unofficial notes on the development of ARPANET. RFCs have since become official documents of Internet specifications.
In computer network engineering, a Request for Comments (RFC) is a formal document published by the Internet Engineering Task Force (IETF), the Internet Architecture Board (IAB), and the global community of computer network researchers, to establish Internet standards. The Internet Engineering Task Force (IETF) develops and promotes voluntary Internet standards,
The IETF started out as an activity supported by the U.S. federal government, but since 1993 it has operated as a standards development function under the auspices of the Internet Society, an international membership-based non-profit organization.
Which came first the Internet model or the ISO model?
A question often asked is which network reference model came first. Various sources state that the ground work for the Open Systems Interconnection model (OSI Model) started in the 1970s by a group at Honeywell Information Systems. Other sources point to two projects that began independently in the 1970s to define a unifying standard for the architecture of networking systems. One was administered by the International Organization for Standardization (ISO), and one by the International Telegraph and Telephone Consultative Committee (CCITT).
RFC 871 published in September 1982 is one of the first formal descriptions of the ARPANET Reference Model (ARM). The the introduction of RFC 871 addresses the history of the internet model versus the ISO model.
"Since well before ISO even took an interest in "networking", workers in the ARPA-sponsored research community have been going about their business of doing research and development in intercomputer networking with a particular frame of reference in mind."
Is there an official document that explains the ARPANET Reference Model (ARM)?
RFC 871 was published in September 1982 as a recollection of the past by one of the developers ARPANET Reference Model as the author describes "as a perspective on the ARM." The author points out that the ARPANET Network Working Group (NWG), which was the collective source of the ARM, hasn't had an official general meeting since October 1971.
The four layer internet was defined in Request for Comments 1122 and 1123. RFC 1122, published October 1989, covers the link layer, IP layer, and transport layer, and companion RFC 1123 covers the applications layer and support protocols
The TCP/IP Model is not merely a reduced version of the OSI Reference Model with a straight line comparison of the four layers of the TCP/IP model to seven layers of the OSI model. As you read through many of the RFC documents on the IETF protocol development you will see direct statements that they are not concerned with strict layering such as section 3 of RFC 3439 which is titled: "Layering Considered Harmful."
The links below to RFC 1958 and 3439 will help you understand the general mindset of the developers of TCP/IP. RFC 1122 and RFC 1123 are the definitions of the four protocol layers of the TCP/IP model. As the constantly growing library of RFCs illustrates, the concept of the TCP/IP is a ongoing evolution.
Request for Comments (RFC) http://www.ietf.org/rfc.html
Memos in the Requests for Comments (RFC) document series contain technical and organizational notes about the Internet. The Internet Engineering Task Force (IETF) is a large open international community of network designers, operators, vendors, and researchers concerned with the evolution of the Internet architecture and the smooth operation of the Internet.
RFC 871: September 1982 https://tools.ietf.org/html/rfc871
A perspective on the ARPANET REFERENCE MODEL
Abstract: The paper, by one of its developers, describes the conceptual framework in which the ARPANET intercomputer networking protocol suite, including the DoD standard Transmission Control Protocol (TCP) and Internet Protocol (IP), were designed.
RFC 1122: October 1989 https://tools.ietf.org/html/rfc1122
This RFC covers the communications protocol layers: link layer, IP layer, and transport layer;
RFC 1123: October 1989 https://tools.ietf.org/html/rfc1123
This RFC covers the applications layer and support protocols.
RFC 1958: June 1996 https://tools.ietf.org/html/rfc195
Architectural Principles of the Internet
RFC 3439: December 2002 https://tools.ietf.org/html/rfc3439
Internet Architectural Guidelines
Extends RFC 1958 by outlining some of the philosophical guidelines to which architects and designers of Internet backbone networks should adhere.
Links to learn more:
Check out our site Geek History where we discuss the evolution of the ARPANET and TCP/IP
Why was the internet created: 1957 Sputnik launches ARPA
When was internet invented: J.C.R. Licklider guides 1960s ARPA Vision
In the 1960s Paul Baran developed packet switching
The 1980s internet protocols become universal language of computers
Photo: Interface Message Processor (IMP) ARPANET packet routing